一种用于RM不稳定性研究的竖直环形激波管的设计与验证

Design and validation of a vertical annular shock tube for RM instability study

设计并加工了一套竖直环形同轴无膜激波管,可用于环形汇聚激波诱导下的Richtmyer-Meshkov不稳定性实验研究。与前人工作相比,本文在流体界面的形成以及流场的观测方法上做了较大的改进。通过实验和数值方法,对该竖直激波管产生的环形柱状汇聚激波的参数进行测量和分析,验证了同轴激波管形成柱状汇聚激波方法的可行性和可靠性。在界面形成方面,采用细丝约束肥皂膜技术形成正八边形气体界面,并利用数值方法考察了细丝对界面发展的影响。结果表明在界面发展的前期,细丝的影响几乎可以忽略。利用连续激光片光结合高速摄影相机对流场进行观测,获得了正八边形air/SF6气体界面在环形汇聚激波及其反射激波冲击下的演化过程,并与数值结果进行了对比,获得了较好的一致性,进一步验证了汇聚激波的对称性以及细丝约束肥皂膜技术用于形成多边形气体界面的可靠性。

A vertical annular coaxial diaphragm-less shock tube is designed based on the prin-cipal proposed by Hosseini and Takayama and modified in order to conveniently install the initial interface in the test section and visualize the flow field for the investigation of the Richtmyer-Meshkov （RM）instability.Parametric study is carried out both experimentally and numerically to explore the characteristics of the annular coaxial cylindrical converging shock wave.The varia-tion of pressure behind the shock shows the feasibility and reliability of this shock tube to generate the annular coaxial cylindrical converging shock wave.The pressure variations with time at differ-ent positions in the test section are acquired from the experiment and numerical simulation,and the converging effect of the shock wave is emphasized.After the validation of the converging shock wave,the experiment of RM instability induced by this converging shock wave is con-cerned.For this purpose,a regular octagon air/SF6 interface （the distance from each vertex to the center is 20mm）is generated in the test section by using eight thin wires to restrict the soap films.In this way,the initial interface shape,which is crucial to RM instability study,can be precisely controlled.The influence of the thin wires on the interface evolution is also assessed by numerical simulation and the results indicate that the thin wires have limited effect on the inter-face development at the very early stage.Moreover,because the height of the interface generated is only 5mm,the influence of the gravity can be neglected and the regular octagon soap interface can be treated as two dimensional.For visualizing the flow field,a continuous laser sheet combined with the high-speed camera is employed and the evolution of the regular octagon air/SF6 interface accelerated by the annular coaxial converging shock wave and its reflected shock wave is captured through the Mie scatting light from the droplets of the soap film.Corresponding numerical simulation is also performed for comparing with the experiment,and a good agreement is found between these two results.During the evolution,the inter-face is first compressed after the incident converging shock wave passage and then the “spike”and “bubble”configurations are generated due to the deposition of the baroclinic vorticity on the interface.Phase reversal occurs on the interface after the reflected shock wave impacts on it,which creates an opposite pressure gradi-ent compared with the initial incident shock.The secondary “spike”configuration is generated at the original“bubble”position while the secondary“bubble”configuration is generated at the original“spike”position and they grow gradually with time.From the observation,it can be found that the interface evolution is quite symmetric which once again verifies the reliability of the shock tube to generate the converging shock wave and the interface formation method.